1. Field
This disclosure relates to a positive electrode for a rechargeable lithium battery and a rechargeable lithium battery including the same.
2. Description of the Related Art
Lithium rechargeable batteries have recently drawn attention as a power source for small portable electronic devices. They use an organic electrolyte solution and thereby have twice the discharge voltage of a conventional battery using an alkaline aqueous solution, and accordingly have high energy density.
For positive active materials of a rechargeable lithium battery, lithium-transition element composite oxides being capable of intercalating lithium, such as LiCoO2, LiMn2O4, LiNi1−xCoxO2 (0<x<1), and so on, have been researched.
As for negative active materials of a rechargeable lithium battery, various carbon-based materials such as artificial graphite, natural graphite, and hard carbon, which can intercalate and deintercalate lithium ions. However, the carbon-based negative active material generates irreversible capacity; lithium corresponding to the irreversible capacity of the negative electrode is deficient in a positive electrode; and potential (Li/Li+) of positive electrode is increased. The increasing potential of positive electrode may deteriorate the cycle-life.
Recently, the demands on a high energy density battery are increasing. For this purpose, there are attempts to use the negative active material including Si, Sn, Ge, the oxide thereof, or the alloy thereof capable of being alloyed with lithium having a higher theoretical capacity density than carbon-based material. However, the negative active material generally has inferior initial efficiency than the graphite negative active material, and it may generate the irreversible capacity that lithium inserted during the initial charge and discharge is not deintercalated during the discharge.
In addition, in the high power battery for an automobile or the like, amorphous carbon (Hard Carbon etc.) is considered as a negative active material since it has high power-high input characteristics. However, the amorphous carbon negative active material has bad discharge efficiency to the initial charge compared to graphite, so it may deteriorate the energy density of battery.
All these problems may be caused by the bad initial discharge to the initial charge of negative electrode which is irreversible capacity and by the deterioration of the initial discharge efficiency. In order to improve the irreversible capacity of negative electrode, the following methods are recently reviewed: adhering lithium to negative active material; or using nitride (Li1+xMyN, M is a transition element, x is within a range of −0.2 to 2.0, and y is within a range of 0.1 to 0.5) for a negative electrode.
However, the negative electrode including the lithium or lithium-included material is generally highly reactive with moisture and oxygen in the air and has problems on the safety of manufacturing process, so it is not practical.